Hey, not bad! You make a really cute Mari! Having made this costume myself maybe I can tell you what I used for certain parts of mine to help you with your next one.
I think it's good that you're choosing a 4-way stretch vinyl, that should elevate the polish of it already. Vinyl is kind of a pain to work with but you seem to know what you're doing sewing wise so that should work wonderfully
I think for the red parts of your costume you should sculpt them in 3D form-did you just use fabric for them on the first version? Having them be shiny and "inlaid" into your fabric would really help make the plugsuit look more realistic. For my "armor" parts I used wonderflex with vinyl overtop. It's a bit of a difficult and expensive material to work with-but you can always rework it and it really helped me get the sloped shapes like her shoulders and boob cups haha. I also used foamie, paperclay and cardboard for her other hard parts like her ribs and backpack.
Anyway I hope that helps! I can't wait to see your new version! Give yourself more than a month to make it, I can't imagine how stressful that was the first time around!